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097-55501-01 Revision M – January 2009
TimeHub 5500 User’s Guide 169
Chapter 4 Testing and Configuring the TimeHub
Provisioning the NTP Parameters
The default values for the client mode are as follows:
Polling: Minimum of 16 seconds and a maximum of 1024 seconds
Authentication Key = 0, No MD5 Authentication
Preferred Server = 0, No preferred server
Provisioning for MD5 Authentication
The main purpose of authentication is to detect hacking of the timestamps or other
information in the packet. Clients and secondary servers care about authenticity of
the NTP packets from the servers, because they use the timestamps in the NTP
packets to correct their local clocks. Primary NTP servers don't use other servers'
and clients' timestamps to correct its clock; it supports authentication primarily for
the benefits of clients and secondary servers. Authentication requires that both the
sender and the receiver of the NTP packets share the same keys. User can disable
authentication or specify a chosen key.
You can define up to 16 keys (and their corresponding key IDs) for each TimeHub
NTP card. These 16 keys are shared with all trusted members on the network. In
other words, there are 16 keys for this network.
To enable MD5 Authentication, issue the following commands:
ED-EQPT::S0-OUTA:CTAG:::MKEYID1=<any number from 1-65534>;
ED-EQPT::S0-OUTA:CTAG:::MKEYVAL1=<"string up to 32
characters">;
ED-EQPT::S0-OUTA:CTAG:::NTPPAIR=APPLYCFG;
The key ID and key value numbers must be the same in order to correlate the two.
Provisioning for Traffic Load Limit
The NTP Server card implements traffic control or to prevent the complete loading
down of the NTP card processor from excessive traffic on any NTP port.
When traffic control is not activated, a NTP Server card will accept packets from
both NTP ports on a first-come-first-served basis. When in any one-second interval
the combined traffic loading from port A and port B has reached the packet
processing limit of the card, all subsequent packets will be dropped for the rest of
the one-second interval. The current packet processing limits are 1000
authenticated packets or 1500 unauthenticated packets per one-second interval.
This capacity assumes that the incoming packets are distributed evenly in time.
When traffic limits are used, during each one-second interval the NTP card will
accept from port A a fixed percentage of the card processing capacity limit; the
remaining percentage will be assigned to port B.
To enable traffic load limits, issue the following commands: